1. Field of the Invention
The present invention relates to a method and an apparatus for analyzing vibrations of the housing of a disk device or, in particular, to a method and an apparatus for analyzing vibrations of the housing of a disk device built into a computer, or a locker as an external storage unit for the computer, which vibrations are attributable to a head actuator of the disk device.
2. Description of the Related Art
With the recent increase in the storage capacity of a disk device such as a magnetic disk device used as a storage unit for a computer, the pitch of the data recording tracks (the reciprocal of TPI (Tracks Per Inch)) have been increasingly reduced. As a result, the allowable displacement of the head from an intended track on the magnetic disk (allowable off-track value) has become smaller than ever before. The allowable off-track value is affected also by the vibrations of the housing of the disk device in operation, and therefore it is critical to detect the vibrations of the housing of the disk device in operation. Accordingly, a superior method for analyzing the vibrations of the housing of the disk device is required.
A disk device is built into a computer in some cases. In other cases, however, a plurality of disk devices are used in juxtaposition in a rack (in a locker) external to the computer. In the disk devices used in juxtaposition in the locker, the off-track amount of the head is liable to be affected by the vibration characteristic of the locker depending on the conditions under which it is installed in the premises of the customer.
In order to obviate this problem, a protective measure against the vibrations of the disk device housing has conventionally been taken by mounting a vibration sensor on the locker for detecting the vibration characteristics of the locker.
However, the conventional measures for protection against the vibrations of the disk device housing are unsatisfactory in that the protective measures taken depend solely on the evaluation of the parallel displacement of the locker and the disk device housing.
In the conventional method of evaluating the vibrations of the housing of a disk device, a dummy disk device with a head capable of a seek operation is delivered to the customer, and the off-track amount of the head placed on track is measured. The housing is judged to have no problem if the off-track measurement is not more than a predetermined value on the order of microns. This conventional vibration evaluation method, however, cannot indicate the frequency of vibrations clearly and cannot take any anti-vibration measure in the case where the off-track amount exceeds a predetermined value.
The present inventors have studied this vibration problem of the conventional disk device housing, and have discovered that the locker vibrations originate not only from the motion thereof parallel to the disk devices but by the resonance of the housing caused by the reaction due to the rotation of the head actuator in the disk device. It has also been found that the metal plate of the housing resonates, and that the housing oscillates if fixed insufficiently, and that the rotational displacement of the housing is directly converted into a head oscillation to thereby increase the off-track amount.